When I tell people I'm aiming for a PhD in evolutionary biology, they almost always respond by asking what I will "get" out of the degree. Previously, I've launched into a monologue about how graduate degrees differ from many undergraduate degrees and trade school certificates; that I'm not educating myself for a single position with a range of possible employment opportunities, but rather for a single field with a range of possible positions, each with their own employment opportunities.
Monologue over, the conversation typically devolves into something like...
"Right, but what will you do for a living?"
"I don't understand the question... I'll 'do' evolutionary biology..."
"Oh... So you'll be a teacher or something?"
Not exactly productive, but I've found a solution in meme form:
From now on, I shall simply say, "I'll get some sort of idea what I'm doing."